Such an illumination device is known from U.S. Pat. No. 5,782,551. The known illumination device is a luminaire that is mounted with a backside to a deck. An acoustical shell, which acts as a reflector and which can produce an office light beam with conventional louver optics, is provided at the backside of the luminaire. Said acoustical shell is made such that it allows sound to pass through to an absorbing blanket provided in between the acoustical shell and the deck. To this end the acoustical shell is made from perforated metal material or molded, high-density fiberglass material. The acoustical shell and the absorbing blanket thus form a stack of an optical element and an acoustically absorbing element. This causes the known luminaire to have the disadvantages of being relatively expensive, involving laborious mounting, and having a relatively complicated and rather bulky construction.